Conventional, electric, plug-in connectors are used in commercial fields such as mobile-phone installations. To mount the plug-in connector, the tightening torque with which the union nut is screwed together with the mating connector must lie within a predetermined tolerance range so that a secure electric contact is ensured and mechanical overloading of the structural parts of the plug-in connector and the mating connector is avoided. For this purpose, the union nut has wrench flats for the application of a torque wrench. The question whether the required tightening torque was maintained during mounting or whether a torque wrench was used at all cannot be verified subsequently.
Thus, it would be desirable to provide an electric plug-in connector that can be mounted without a torque wrench.